Can improving biodiversity help reduce greenhouse gas emissions from small waterbodies?

Climate change and the intensification of land use practices are causing widespread changes in ecosystems globally. This is particularly evident in freshwater ecosystems, a critical resource for society, where high connectivity within and between ecosystems allows multiple stressors to degrade these habitats. Small waterbodies, such as ponds, are some of the most numerous freshwaters globally with numbers estimated in the order of three hundred million. In addition, ponds are disproportionately biodiverse and, consequently, numerous schemes exist to create, restore or improve them. However, a growing body of research has also pin-pointed small waterbodies as significant sources of greenhouse gases (GHG) such as carbon dioxide, methane and nitrous oxide (Holgerson & Raymond, 2016). Despite this, little is known about the processes and mechanisms driving GHG release from small waterbodies and therefore the contribution of small waterbodies to the global carbon cycle and GHG emissions remains highly uncertain.

One of the primary aims of pond restoration is the recovery of biodiversity, in particular aquatic plants. Aquatic plants are a fundamental component of aquatic food webs, influencing nutrient flux, physico-chemical quality, biodiversity and hydrodynamics (Andersen, Sand-Jensen, Iestyn Woolway, & Jones, 2017; Law et al., 2019). By influencing the physical habitat of a waterbody (e.g. by mediating temperature variation or mixing from wind action) it is possible that aquatic plants may also regulate GHG emissions, as increased temperatures and mixing of the water column are speculated as drivers of GHG release (Ortega et al., 2019).

Studies on standing waterbodies have indicated high levels of dissolved carbon dioxide (CO2) and methane (CH4) particularly in smaller waterbodies, such as ponds (Figure 1). Further investigation is now required to; (i) identify the underlying drivers, (ii) determine whether high dissolved concentrations translate into emissions and (iii) assess if increased aquatic plant coverage influences GHG release via alterations of the local physical or biochemical environment.

The overall aim of this PhD project is therefore to identify and understand the drivers of greenhouse gas emissions from small waterbodies whilst assessing the potential role that improved biodiversity plays in regulating emissions. This PhD will expand on existing knowledge in restoration ecology to determine if there are additional benefits to the carbon cycle as well as to biodiversity. Fieldwork will be focussed in an agricultural catchment (North Norfolk) studying a suite of ponds across a restoration gradient in a before-after-control-impact (BACI) designed project covering unrestored, newly restored (1-3 years) and long-term restored (> 5 yrs) ponds.